1. Field of the Invention
The present invention relates to a wafer-level lens array, a method of manufacturing a wafer-level lens array, a lens module and an imaging unit.
2. Description of the Related Art
In recent years, portable terminals of electronic apparatuses, such as mobile phones or PDAs (Personal Digital Assistants), include small and thin imaging units. In general, the imaging unit includes a solid-state imaging element, such as a CCD (Charge Coupled Device) image sensor or a CMOS (Complementary Metal-Oxide Semiconductor) image sensor, and a lens for forming an object image on the solid-state imaging element.
With a reduction in the size and thickness of the portable terminal, there has been a demand for a small and thin imaging unit. In addition, it is preferable to make a manufacturing process efficient in order to reduce the costs of a portable terminal. As a method of manufacturing a plurality of small lenses, a method has been proposed which manufactures a wafer-level lens array in which a plurality of lenses is formed on a substrate unit and cutting the substrate unit into a plurality of lenses, thereby mass-producing lens modules.
In addition, a method has been proposed which integrates a substrate having a plurality of lenses formed thereon with a semiconductor wafer having a plurality of solid-state imaging elements formed thereon and cutting the substrate and the semiconductor wafer lens into sets of the lenses and the solid-state imaging elements, thereby mass-producing imaging units.
As a method of manufacturing a wafer-level lens, for example, there is a method of manufacturing a wafer-level lens array using the following processes, which is disclosed in WO 2008/153102 (corresponding to US-A-2010/0181691).
(1) With a resin applied onto a wafer, the shape of one transfer body (mold) is transferred to the resin.
(2) The process of transferring the shape of the mold is repeated about 1500 to 2400 times to form a master lens array having 1500 to 2400 lens shapes on one wafer.
(3) Metal ions, such as Ni ions, are deposited on the lens surface of the master lens array by electroforming to manufacture a stamper (Ni electroforming mold).
(4) The stampers are used as a pair of lens array forming molds and a photo-curable resin or a thermosetting resin is supplied to the lower lens array forming mold of the pair of lens array forming molds.
(5) The upper lens array forming mold presses the supplied resin to deform the resin into a shape corresponding to the forming surfaces of the upper and lower lens array forming molds.
(6) Light or heat is applied to the resin to cure the resin, thereby forming a lens array.
For example, Japanese Patent No. 3926380 and WO 2008/102648 disclose an optical system including a composite lens obtained by bonding a lens unit to a parallel plate substrate.
Japanese Patent No. 3926380 (corresponding to US-A-2009/0279188) relates to the structure of an imaging lens including a composite lens in which lens units are bonded to both sides of a substrate made of a glass material. Japanese Patent No. 3926380 discloses a structure in which the difference between the refractive indexes of the two lens units of the composite lens is in the range of 0 to 0.1 and the difference between the Abbe numbers thereof is in the range of 0 to 30.
WO 2008/102648 (corresponding to US-A-2010/0046096) relates to the structure of an imaging lens including a lens substrate, which is a parallel plate, and a group of lenses that are formed on at least one surface of the lens substrate. WO 2008/102648 discloses a structure in which the difference between the Abbe number of a lens with a positive refractive power and the Abbe number of a lens with a negative refractive power is more than 10.
As in WO 2008/153102, when the substrate unit and the lens unit are integrally formed of the same material, it is inevitable that the resin used as the forming material is cured by light or heat and is shrunken, or it is expanded or contracted due to a temperature variation. When the resin is cured by light or heat and is shrunken, there is a concern that the lens unit will be shrunken in the diametric direction, and the shape of the lens surface will be greatly deformed.
In addition, the resin is not uniformly shrunken, or expanded or contracted in the entire wafer. Therefore, when the wafer-level lens arrays overlap each other or when the wafer-level lens array overlaps the imaging element array, there is a concern that the positional deviation between the lens units will occur due to shrinkage, or contraction or expansion.
As in Japanese Patent No. 3926380 and WO 2008/102648, when the substrate unit of the lens array and the lens unit are made of different materials, light is refracted at the interface between the substrate unit and the lens unit. As a result, the design becomes complicated. When the lens is used as an imaging lens, image quality deteriorates due to, for example, flare caused by the reflection of light from the interface.